I don't think its a hardware mover.
People always think selling hardware is everything. If someone wants to play Mass Effect 2 and buys a 360, plays it and never plays another 360 game... Microsoft doesn't benefit from this at all.
This to me seems like what Mass Effect 2 will do... Its a very core oriented game, and most of those people at this point of the console generation (4 years in for 360) don't have a 360 because they don't wan't one.
I think Mass Effect 2 is one amazing game and it may cause a 10-15 K spike of console sales in the US and 10K in EU...but my hunch is that most of the people that buy a 360 to play this game will either have it collecting dust or will sell it once they are done with Mass Effect 2. Its not a game thats gonna hook anyone in to xbox live or other 360 strenghts...